But to seed all seeds one by one.. It's not fun after some time (after 2 weeks for me personally). 
I like gather my carrot one by one, but gather and then put seeds and then water them - it's too much...It would be great to have possiblity to pay somekind of NPC (lets it would be funny guy hehe) some silver so he would seed all seeds into the field for you.
Also I heard that some baaad players using automatic scripts to seed/harvest at their island.. And there is no way to detect it (nobody can report there, they are alone). If there would be option to seed all seeds at once - this behavoir wouldn't be popular
Double profit!